The present invention relates to a procedure and an apparatus, relating to the connection between a data terminal means and a radio telephone.
The modern digital cellular systems offer the user a great number of services in addition to standard call transmission. For instance, in the Global Systems for Mobile phones (GSM) system the services have been classified into three classes: telecommunications, bearer and auxiliary services.
The telecommunications services are services which are available to the network subscriber. They enable data transfer between the users according to agreed communications practices, i.e. protocols. In addition to transmission of telephone calls, the GSM standard includes the following telecommunications services: emergency call, automatic fax group 3, and short message service.
The bearer services make the use of the telecommunications services possible. They are divided into the following classes: circuit switched asynchronic data transfer, circuit switched synchronic data transfer, Packet Assembly Disassembly (PAD) communication as asynchronic data transfer, packet switched data, and exchangeable speech/data transfer.
The services are defined to be transparent and non-transparent. A transparent service is not provided with flow control, and the error ratio thereof varies in accordance to the mode of the radio channel. A non-transparent service includes a flow control and a specific Radio Link Protocol RLP, provided with an Automatic Repeat request ARQ, whereby the delays vary but the error ratio is low.
When data services specified in digital cellular systems are used, they and the transfer protocols associated therewith require a considerable amount of processing capacity, as well as program and data memory capacity of the mobile phone, because a data terminal connected to the phone, such as a facsimile device or a personal computer, uses data transfer protocols of its own, which in the phone have to be adapted to the protocols of the cellular system to be used.
PCT Application WO 93/02512 describes a common radio telephone part comprising a transceiver, a speech coder, a microprocessor unit with a memory, and a data arrangement block. A plurality of peripherals can be connected to the common part via a data bus. The bus is a cable in which time division multiplexed data transfer on a data bus is carried out between the part in common and the peripherals. Each peripheral part also includes a data arrangement block which formats the digital data produced by the part and positions it in an appropriate time interval of the bus. In the application aspects associated with bus management are described in detail, such as priority and control of collisions. There is no discussion of the respective functions of the common and peripheral parts. The peripheral part refers primarily to separate operating means (handset + keyboard + speech codec). A plurality of calls travel via one transceiver.
In WO 93/02512 a modern phone is described as including functions supporting data transmission, such as a radio unit, the rf frequencies thereof being those used in said system, and an interface between the radio unit and the other functions; a system-specific signalling towards the network and from the network to the phone (such as call control) and other control functions, such as user connection; and a system-specific coding/decoding and potentially error correction of the data travelling via the radio interface to the traffic channel and therefrom.